Method and apparatus for providing redundant I/O adapters in machine and process controllers

ABSTRACT

Methods and apparatus for redundancy in machine or process control systems provide redundant communication adapters located with the groups of I/O modules, so that if the first communication adapter faults or becomes unavailable, a second communication adapter will perform all of the necessary functions of the first adapter. The adapters are connected to a multiplexing module for communicating input data from the I/O modules to the communication adapters, for exchanging initialization data with the first communication adapter and the second communication adapter to initialize the redundant mode of operation and for monitoring communication of the first communication adapter and the second communication adapter on the network to start up the second adapter as the primary adapter for communicating both input data and output data with the I/O modules.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable

TECHNICAL FIELD

The field of the invention is control systems for controlling theoperation of machines and processes.

BACKGROUND ART

Machine and process controllers include a controller processor and I/Omodules, the latter connecting to I/O devices on a machine or process.The term “I/O modules” is a general classification that includes inputmodules that receive signals from input devices such as photo-sensorsand proximity switches, output modules that use output signals toenergize relays or to start motors, and bidirectional I/O modules, suchas motion control modules which can direct motion devices and receiveposition or speed feedback. Early I/O modules converted between AC andDC analog signals used by devices on a controlled machine or process and+5-volt DC logic signals used by the controller. Later I/O modulesprovided digital signals to digital I/O devices and received digitalsignals from digital I/O devices. Some I/O modules that are used tocontrol motion devices or process control devices require localmicrocomputing capability on the I/O module.

Input data is collected from I/O modules and communicated to thecontroller processor. The controller processor performs logic operationson the input data to produce output data which is then communicated backto the I/O module having output capability. Controller processors havegrown in computational ability and thus have increased communicationrequirements to larger groups of remotely located I/O devices. This hasresulted in the common use of communication scanners and adapters. AnI/O scanner is located near the controller processor and interfaces thecontroller processor through a distributed I/O network having aplurality of remote locations which can be at great distances from thecontroller processor. At various locations in the network, collectionsof I/O modules are interfaced in groups to the network by acommunication adapter module known as an I/O adapter.

Originally one group of controller products was developed for machineand assembly line control, while another group of controller productswas developed for process control. With the advances in microelectronicsand microcomputers, the product lines are becoming suitable for bothtypes of applications.

In process control, such as in the food and beverage industry, or in thepetrochemical industry, there is a need for redundancy of systems toavoid an interruption in operation that would lead to a loss of theprocess batch. In machine and assembly line control, control systemsmust be designed so as to avoid down time. In many computer operations,there is a need for redundancy. Quite often this has led to completeredundancy of computers, using a primary computer and a backup computeroperating in tandem.

Flood et al., U.S. Pat. No. 5,777,874, issued Jul. 7, 1998, disclosed aprogrammable controller backup system in which a primary controllerprocessor was linked with a backup controller processor, each processorhaving an associated I/O scanner for communicating over a network togroups of I/O modules. If the primary controller processor becameunavailable, control was shifted to the backup controller processor andits I/O scanner.

Flood, U.S. Pat. No. 5,912,814, issued Jul. 15, 1999, addressed afurther problem in such a backup system in which the input data in theI/O table in the backup controller processor is not as current as theinput data in the I/O table data in the primary controller processor.This can result in the output devices being set to a prior state at thetime of changeover to the backup system and followed by a return to thepresent state and this is known as a “data bump.” The Flood '814 patentprovides a solution for bumpless switching from the primary controllerprocessor to the backup controller processor.

The provision of redundant controller systems is a solution withsubstantial cost in terms of equipment. It would be advantageous toprovide redundancy in other ways that would be less costly and moredirectly related to the type of faults that may occur in controllersystems.

SUMMARY OF THE INVENTION

The present invention relates generally to methods and equipment forproviding redundancy or backup in machine or process control systems.The present invention provides redundant I/O adapters located with thegroups of I/O modules for interfacing the I/O modules to a distributedcontroller data I/O network. If the first communication adapter faultsor becomes unavailable, a second communication adapter will perform allof the necessary functions of the first adapter.

The adapters are connected to a multiplexing module. The multiplexingmodule communicates data to and from the I/O modules to thecommunication adapters. The multiplexing module also exchangesinitialization data with the first communication adapter and the secondcommunication adapter to initialize a redundant or backup mode ofoperation. And, the multiplexing module monitors communication of thefirst communication adapter and the second communication adapter on thecontroller data I/O network. If the first adapter stops communicating,the multiplexing module starts up the second adapter as the primaryadapter for communicating both input data and output data with the I/Omodules.

The multiplexing module assists in the switchover from the firstcommunication adapter to the second communication adapter. Themultiplexing module allows the second communication adapter to updateinput data from the I/O modules so as to avoid data bumps, beforecommunicating any output data to the I/O modules.

In a further aspect of the invention, the multiplexing module isinserted between the first communication adapter and its associated I/Omodules and is connected to the second adapter through a serial datacable.

The I/O adapters operate at the same network address on the controllerdata I/O network and are updated during an I/O scan performed by an I/Oscanner at the head end of the network. The second communication adapterwill be transparent to the controller processor, I/O scanner and otherupstream nodes on the network, which will not detect which communicationadapter is the primary adapter at any give time.

The invention will enable one to provide backup adapters for severaltypes of I/O module product lines having different types of electricaland physical characteristics.

These and other objects and advantages of the invention will be apparentfrom the description that follows and from the drawings which illustrateembodiments of the invention, and which are incorporated herein byreference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view in elevation of one configuration of I/Oequipment for carrying out the present invention;

FIG. 2 is a block diagram of a prior art system using a backupcontroller processor and I/O scanner;

FIG. 3 is a block diagram showing a modification made to FIG. 2according to the present invention;

FIG. 4 is a block diagram of a multiplexing module of the presentinvention;

FIG. 5 is a block diagram of an I/O adapter of the present invention;

FIG. 6 is a generalized block diagram of one of the I/O modules utilizedin the present invention;

FIG. 7 is a diagram of the messages communicated between the adapter andthe multiplexing module;

FIG. 8 is a flow chart of the operation of the adapters in initializinga redundant adapter mode of operation;

FIG. 8 a is a detail view of the switches for setting addresses on theadapter modules of the present invention;

FIG. 9 is a flow chart of the bumpless switchover from a primary adapterto backup adapter according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a front view in elevation of one configuration of I/Oequipment 10 for carrying out the present invention. I/O modules 11 aremounted on terminal bases 12, which in turn are mounted on a DIN rail13. These items are commercially available under the trade designation1794 Flex I/O from the assignee of the present invention. While thepreferred embodiment is described in relation to this product line, theinvention can also be applied to other I/O product line configurationsincluding, but not limited to: 1769 Compact I/O, 1756 ControlLogix I/Oand 1734 Point I/O product lines of the assignee herein.

The I/O modules 11 offer provide circuits for I/O data points in a rangefrom four to thirty-two for each module. There are up to eight I/Omodules 11 for each I/O group 10 providing up to two hundred andfifty-six data points per assembly. The I/O modules 11 not only pluginto module terminal bases 12 but also plug into each other at the ends.The module terminal bases 12 provide a backplane that forms a serialdata I/O bus and also provide terminals 14 on the front side forconnecting via I/O wires to I/O devices on a controlled machine orprocess. A conventional I/O adapter module would plug into an endterminal base on the DIN rail 13, which would plug into the terminalbase 12 for the I/O module 11.

In the present invention, a multiplexing module 16 is plugged into abase on the DIN rail 13 next to the I/O module 11. A master adaptermodule 15 is plugged into an end terminal base that is mounted on theDIN rail 13 and is connected on one end to the base for the multiplexingmodule 16. In addition, the multiplexing module 16 has a serial busconnector 19 which can be connected through a cable 20 to a similarconnector 21 on a backup or redundant adapter module 22. The masteradapter 15 and the backup adapter 22 have respective connectors 15 a and22 a for receiving a network connector for one of a plurality ofpossible controller data I/O networks 27 available from the assigneeunder the trade designations Ethernet/IP, ControlNet, Local I/O orUniversal Remote I/O, and other networks known in the art, whichcommunicate data with a controller processor 25. Typically, thesenetworks are serial data networks that utilize serial data methods andprotocols. This connection of the adapters 15 and 22 to the selectedcontroller data I/O network 27 (FIG. 2) allows the adapters 15 and 22 toreceive output data from the I/O scanner 26 during an I/O scan operationof a type that is well known in the art.

A block diagram of the control system prior to the present invention isshown in FIG. 2. A controller processor 25 interfaces to the controllerdata I/O network 27 through a network I/O communication scanner module26. The controller data I/O network 27 connects to three I/O groups atlocations of various distances from the controller processor 25 througha network cable to three I/O communication adapters 29, 30 and 31. Theseadapters 29-31 communicate I/O data through a backplane to and fromgroups of I/O modules 32, 33 and 34. The I/O modules 32-34 in turnconnect to groups of I/O devices 35, 36 and 37 on a controlled machineor process.

FIG. 2 shows the added feature of the prior art in providing a backup orredundant controller processor 23 and a redundant network I/Ocommunication scanner 24. Flood et al., U.S. Pat. No. 5,777,874, issuedJul. 7, 1998, disclosed a programmable controller backup system in whicha primary controller processor was linked with a backup controllerprocessor, each processor having an associated I/O scanner If theprimary controller processor became unavailable, control was shifted tothe backup controller processor and its I/O scanner.

FIG. 3 shows a modification to this arrangement made by the presentinvention. In this case, there is no backup or redundant controllerprocessor and there is no redundant network I/O communication scanner,however these could be utilized in addition to the present invention.The present invention, however, utilizes a master I/O adapter 15connected to the multiplexing module 16. The multiplexing module 16connects to a terminal base 18 which forms the I/O bus 38 in the regionbetween a master I/O adapter 15 and its associated I/O modules 32. Themultiplexing module 16 is, in turn connected to a backup I/O adapter 22,through a multiplexing module cable 20, which can be a serial data cableor a parallel data cable. The backup I/O adapter 22 also receives serialdata through the controller data I/O network 27.

FIG. 4 shows a block diagram of the multiplexing module 16. The modulehas two application specific integrated circuits (ASICs) identified hereas ASIC 1 and ASIC 2. Each of these circuits has lines (I/O BUS1, I/OBUS 1′) for connecting through an I/O bus to a respective one of theadapters 15, 22.

The multiplexing module 16 will reside in the first I/O module positionand will have a unique ID number. The firmware in the redundant adapters15, 22 will switch into a redundant adapter mode of operation when theydetect this specific ID number. ASIC 1 and ASIC 2 will communicate datawith each other via data ports. Preferably, these handle serial butparallel data transfer can also be used here. The 8051 CPUs inside theASIC 1 and ASIC 2 will determine which adapter 15, 22 is functionallyconnected to the I/O modules 32 seen in FIG. 3. To perform this task, adevice such as the EEPROM is provided to store programmed logic that canbe loaded into application specific integrated circuits, ASIC 1 and ASIC2.

Information can be transmitted from the master adapter 15 to the backupadapter 22 through the application specific integrated circuits, ASIC 1and ASIC 2. When the master adapter 15 detects the multiplexing module16, it will send the required information to the associated ASIC 1,which will pass the information to ASIC 2. ASIC 2 will reply to ASIC 1.

Because the multiplexing module 16 is an extra module on the I/O bus 38in FIG. 3, a “Reset-L” signal will be used to select one of two sets ofeight virtual I/O modules, while still performing a slightly modifiedversion of the Reset-L function. Virtual I/O modules are logicalrepresentations in memory of the physical I/O. As a result, this line isdesignated as ADDR/RESET-L line. The ADDR/RESET-L signal will nowcontinually change state when the module 16 is functioning in theredundant adapter mode.

When the ADDR/RESET-L is high, the multiplexing module 16 will selectthe standard eight virtual I/O modules for communication with theadapter 15. When the ADDR/RESET-L is low for more than a time frame suchas 20 ms, the multiplexing module 16 will transmit a RESET signal to thephysical I/O modules. Also, the multiplexing module 16 will issue animmediate RESET signal to the physical I/O modules whenever ahigh-to-low transition occurs on the ADDR/RESET-L line and a SELECTsignal is active. When the ADDR/RESET-L line is low for a time less thana time frame such as 20 ms, then the multiplexing module 16 willde-select the standard eight virtual I/O modules and will select asecond set of virtual I/O modules. The multiplexing module 16 will belocated at the address for the first module in this second set ofvirtual I/O modules.

FIG. 5 shows a block diagram for the adapter modules 15, 22. Eachadapter module 15, 22 has a CPU 40, a non-volatile program memory 41, aread/write data memory 42 and a backplane ASIC 43 for interfacing to theI/O bus 38. There is also a network interface ASIC 44 for interfacing tothe controller data I/O network 27 through a controller network physicallayer interface 47 which may include, for example, a hybrid transceiver,two signal conditioning circuits and connectors for two channels.

A typical physical I/O module is seen in FIG. 6. The physical I/O module11 may optionally include a microelectronic CPU 50 for controllinghigher capacity data exchanges with I/O devices. The I/O module 11typically provides physical and electrical isolation through anisolation interface 52 typically provided by opto-isolator circuits 53.A logic circuit 51 interfaces the I/O bus 38 to the module. Data istypically held in latches 54 on the machine or process side of theisolation interface 52. This data represents the state of input devicesin the case of input data or controls the state of output devices in thecase of output data. Typically, signal conditioning buffers 55 areprovided between the latches 54 and the terminals 14 for connecting toI/O devices.

As represented in FIG. 7, upon powering up, the adapters 15, 22 and themultiplexing module 16 exchange messages with the adapters 15, 22sending a first message and the multiplexing module 16 sending a replymessage.

As seen in FIG. 8, a start up operation involving the adapters 15, 22and the multiplexing module 16 is initiated on power up as representedby start block 60. Then, the adapters send messages to determine if amultiplexing module 16 is present as represented by decision block 61.If no multiplexing module 16 is present, then the remainder of theinitialization process in FIG. 8 is skipped as represented by processblock 62. If a multiplexing module 16 is present, then a check is madefor a proper ID address being returned in a reply message 58 from themultiplexing module 16. If the master adapter receives this message, asrepresented by the first branch from decision block 63, it proceeds tocheck for a match of the address switch settings between the masteradapter 15 and a backup adapter 22. Each adapter 15, 22 has a DIP switchor thumbwheel switch 15 b, 22 b which is set by the user to determineits I/O address. These addresses could also be programmed in a memory soas make the external switches unnecessary. The master adapter 15 and thebackup adapter 22 are arranged to operate from the same address in thisembodiment, with the backup adapter 22 being transparent to the network27. The upstream nodes on the network, such as the I/O scanner 26 andthe controller processor 25, are not signaled when a secondcommunication adapter is installed at said network communication addresson the serial data I/O network. If the switch settings agree asrepresented by the “Yes” result from decision block 64, then the backupadapter is initialized, as represented by process block 66. If theswitch settings do not agree as represented by the “No” result fromdecision block 64, then the backup adapter is not initialized, asrepresented by process block 65. The backup adapter 22 also checks forthe proper ID from the multiplexing module as represented by the secondbranch from decision block 63, and also checks for proper switchsettings relative to the master adapter 15 as represented by blocks64-66. When a backup adapter has been initialized, the I/O assembly 10is operating in a redundant mode.

Referring to FIG. 9, during operation in the redundant mode, there is a“hot backup” mode in which a bumpless data switchover is executed, Inthe redundant mode, the network interface ASIC in the backup adapter 22monitors network traffic from the master adapter 15 as represented bystart block 69. When it stops hearing from the master adapter 15, asrepresented by the “Yes” result from decision block 70, it starts up thebackup adapter 29 operating on the network, as represented by processblock 71. It should be noted that upstream nodes on the network are notsignaled when the second communication adapter becomes the primarycommunication adapter for communicating with the I/O modules. To providefor bumpless transfer of the I/O modules, it causes input data to beread, as represented by I/O block 72, before transmitting any outputdata to the I/O modules during regular communication, represented byprocess block 73. Generally, output data in the master adapter 15 andthe backup adapter 22 are of the same time reference, and it is inputdata which may be more current in the master adapter 15 than the backupadapter 22. When the master adapter 15 comes back online, as representedby the “Yes” result from decision block 74, the master adapter 15signals the backup adapter 22 to stop communicating (via themultiplexing module 16) as represented by process block 75. This willallow the network interface ASIC 44 on the master adapter 15 to startcommunicating on the network 27 as the master adapter 15 returns tocontrolling the I/O modules 11.

Thus, from the above description it should now be apparent how redundantI/O adapters can be located with the groups of I/O modules, so that ifthe first communication adapter faults or becomes unavailable, a secondcommunication adapter will perform all of the necessary functions of thefirst adapter.

The description has included details of how to initialize the redundantmode of operation, and how to monitor communication of the firstcommunication adapter and the second communication adapter on thenetwork and how to start up the second adapter as the primary adapterfor communicating both input data and output data with the I/O modules.

The description has further described how the second communicationadapter, when switching over to control the I/O modules, updates inputsdata from the I/O modules so as to avoid data bumps.

This has been a description of several preferred embodiments of theinvention. It will be apparent that various modifications and detailscan be varied without departing from the scope and spirit of theinvention, and these are intended to come within the scope of thefollowing claims.

1. Apparatus for interfacing I/O modules having terminals accessible forattaching I/O wires to an I/O device on a controlled machine to acontroller data I/O network in a machine or process control systemhaving an industrial controller executing a stored program to controlthe machine or process, the apparatus comprising: a first communicationadapter having a mounting surface and an electrical connection on asidewall perpendicular to the mounting surface to communicate with theindustrial controller through the controller data I/O network; amultiplexing module having a mounting surface, a first electricalconnection on a first sidewall perpendicular to the mounting surface tomate with the electrical connection of the first communication adapter,and a second electrical connection on a second sidewall parallel to thefirst sidewall to allow the first communication adapter to communicatewith the I/O modules, the multiplexing module including a serial busconnector; and a second communication adapter having a mounting surface,an electrical connection on a side wall perpendicular to the mountingsurface and connected to a cable connecting to the serial bus connectorof the multiplexing module and configured to provide an interfacebetween the controller data I/O network and the machine or process, anetwork interface circuit configured to communicate with the industrialcontroller through the controller data I/O network; and an I/O data businterface circuit for communicating with the I/O modules through an I/Odata bus; wherein said second communication adapter and said firstcommunication adapter receive output data from the controller throughthe controller data I/O network; wherein said second communicationadapter and said first communication adapter each transmit output datathrough the I/O data bus when enabled as a primary communication adapterfor the I/O modules, wherein in a redundant mode of operation, themultiplexing module monitors the network to determine that the firstcommunication adapter has stopped communicating and that the secondcommunication adapter should become the primary adapter forcommunicating with the I/O modules, and wherein the multiplexing moduleis connected to the I/O data bus in a position between the firstcommunication adapter and the I/O modules.
 2. The apparatus of claim 1,wherein the multiplexing module is connected for communication with thesecond I/O adapter through one of a serial data cable and a paralleldata cable.
 3. The apparatus of claim 1, wherein the mounting surfacesare configured to mounting to a DIN rail.
 4. The apparatus of claim 1,wherein the first communication adapter is located at a specific addresson the controller data I/O network, and the second communication adapteris located at the address on the controller data I/O network of thefirst communication adapter, as determined by switch settings on thefirst communication adapter and the second communication adapter.
 5. Theapparatus of claim 1, wherein data is exchanged between the multiplexingmodule and each of the first communication adapter and the secondcommunication adapter to initialize the first communication adapter andthe second communication adapter in the redundant mode of operation. 6.The apparatus of claim 1, wherein upstream nodes on the I/O network arenot signaled when a second communication adapter is installed at thenetwork address of the first communication adapter on the controllerdata I/O network nor when the second communication adapter becomes theprimary communication adapter for communicating with the I/O modules. 7.The apparatus of claim 1, wherein the first communication adapter islocated at a specific address on the controller data I/O network, andthe second communication adapter is located at the address on thenetwork of the first communication adapter.
 8. The apparatus of claim 1,wherein determination of which communication adapter is the primarycommunication adapter for communicating between the I/O modules and thecontroller data I/O network is made through exchanging control databetween a multiplexing module and each of the first communicationadapter and the second communication adapter.